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Journal of Clinical Microbiology, September 2001, p. 3115-3121, Vol. 39, No. 9
Department of Microbiology, Kitasato University School of
Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa
228-8555,1 and Laboratory of Drug
Resistance in Bacteria, Gunma University School of Medicine,
3-39-22 Showamachi, Maebashi, Gunma 371-8511,2
Japan
Received 29 January 2001/Returned for modification 31 March
2001/Accepted 15 June 2001
A multiple-primer PCR was used to identify genes encoding
aminoglycoside-modifying enzymes in 381 clinical isolates of
methicillin-resistant Staphylococcus aureus (MRSA). The
technique used three sets of primers delineating specific DNA fragments
of the aph(3')-III, ant(4')-I, and
aac(6')-aph(2") genes, which influence the MICs of
gentamicin, tobramycin, and lividomycin. Isolates with none of the
three genes detected were susceptible to all three agents. Isolates
with the aph(3')-III gene showed resistance to lividomycin (MIC > 1,024 µg/ml), and those with the ant(4')-I
gene were resistant to tobramycin (MIC
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.9.3115-3121.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Identification of Aminoglycoside-Modifying Enzymes by
Susceptibility Testing: Epidemiology of Methicillin-Resistant
Staphylococcus aureus in Japan
8 µg/ml). Isolates
with only the aac(6')-aph(2") gene were resistant to
gentamicin (MIC
8 µg/ml) and tobramycin in decreasing order;
those with both the ant(4')-I and
aac(6')-aph(2") genes also were resistant to gentamicin and
tobramycin, but in increasing order. Susceptibility testing, then,
could detect specific genes. In 381 Japanese MRSA isolates, the
ant(4')-I, aac(6')-aph(2"), and aph(3')-III
genes were prevalent in 84.5, 61.7, and 8.9%, respectively. Isolates
with only the ant(4')-I gene had coagulase type II or III,
but isolates with both the ant(4')-I and
aac(6')-aph(2") genes included all coagulase types. Most
isolates with coagulase type IV or VII carried the
aac(6')-aph(2") gene. Of the MRSA isolates with
ant(4')-I and/or aac(6')-aph(2") genes, 97%
were resistant to aminoglycosides in clinical use, but a new
aminoglycoside, arbekacin, had excellent activity against these isolates.
*
Corresponding author. Mailing address: Department of
Microbiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan. Phone: 81-42-778-9355. Fax: 81-42-778-9350. E-mail: matsu{at}kitasato-u.ac.jp.
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